There was a time early in the history of the USA that presidential candidates did not do any campaigning. Their supporters campaigned but the candidate did not.
The radio caused the mellifluous nature of the voice combined with a confident cadence to become a trait which influenced voters. Beginning with the 1960 election, being photogenic and having stage presence also became factors which influenced voters.
It would be interesting (although unfeasible) to see what would happen if both physical presence and broadcast media (including internet media) were removed from the equation. But the only way that would happen is if a major disaster disrupted our national infrastructure to a degree much more severe than the Covid-19 is currently causing on a global basis.